1. Field of the Invention
The present invention relates to a zoom lens barrel, and more precisely, relates to a zoom lens barrel in which a change in focal length during zooming is detected by a zoom code plate together with zoom brushes which come into contact with the code plate, so that focal length data thus detected can be transmitted to a camera body through a flexible printed circuit (FPC) board.
2. Description of Related Art
For example, in a known zoom lens barrel having a cam ring which is rotated to effect the zooming, the change in focal length caused by the zooming is detected by a zoom code plate secured to a stationary ring of a camera together with zoom brushes which come into slide contact with the code plate during the rotation of the cam ring. The zoom code plate is provided with a predetermined pattern of contacts (contact pattern). Upon zooming, the zoom brushes are rotated together with the cam ring to come into slide contact with the zoom code plate, so that the focal length data corresponding to the focal length can be sent to a drive control circuit of the camera. Consequently, data necessary to control the camera is selected from each of a plurality of data tables of variable information and input to the drive control circuit of the camera body, in accordance with the focal length data.
In the known zoom lens barrel as mentioned above, in which the focal length data detected by the detecting means (zoom code plate together with zoom brushes) is sent to the drive control circuit of the camera body through the FPC board which is connected to the zoom brushes, the zoom brushes are soldered to the FPC board. The soldering is however, troublesome and costly.
Furthermore, since the control data corresponding to the detected focal length data is selected from each data table of variable information and is input to the drive control circuit of the camera body in accordance with the focal length data detected, it is absolutely necessary to accurately dispose the zoom brushes and the zoom code plate in predetermined reference positions. Otherwise, the angular position of the cam ring relative to the stationary ring of the camera body would not be accurately determined, thus resulting in a failure to detect a correct focal length during zooming.
Moreover, in a conventional zoom lens barrel, the zoom code plate is circumferentially secured to the outer peripheral surface of the stationary ring, and the zoom brushes secured to the cam ring are rotated on the zoom code plate in the circumferential direction of the stationary ring. Consequently, it is very difficult to establish an accurate and optimal relative position of the zoom code plate and the zoom brushes by a fine adjustment, for example, upon assembling. To this end, it is necessary to make the shape and position of the zoom code plate and the zoom brushes extremely precise, thus resulting in an increase of the manufacturing cost thereof.
In addition to the foregoing, since the operation of the camera is controlled in accordance with the focal length data detected by the zoom brushes which are brought into slide contact with the zoom code plate, the zoom brushes must be pressed against the zoom code plate at a constant predetermined pressure to accurately read the signals. This, however, requires an expensive and complex arrangement in the conventional zoom lens barrel.